Oupost was one of the many firewall software I used in the past (right now using Comodo, also free of charge). Agnitum firewalls have always been known by their robustness and pro-active security so the free version shouldn’t be any different.

Outpost Free Firewall

This one will be on my “To-Try List” in place of Comodo after I reinstall Windows (in a near near future).